Weather sealed and shielded double door construction for radio frequency shelters



Aprll 1 1964 c. E. WATT, JR.. ETAL 3,129,278

WEATHER SEALED AND SHIELDED DOUBLE DOOR CONSTRUCTION FOR RADIO FREQUENCY SHELTERS 2 Sheets-Sheet 1 Filed Jan. 30, 1965 23 I ,wlllll FIG. I

mviimons CHARLES E. WATT, JR. BY CHARLES J. CARSON EE/m ATTORNEYS April 14, 1964 c. E. WATT, JR.. ETAL 3,129,278

WEATHER SEALED AND SHIELDED DOUBLE DOOR CONSTRUCTION FOR RADIO FREQUENCY SHELTERS 2 Sheets-Sheet 2 Filed Jan. 30, 1963 INVENTORS CHARLES E. WATT, JR. CHARLES J. CARSON v. m. a M mm m 3 A :i'nli nnflmmmm 4 FIG. 3

FIG.

ATTORNEYS United States Patent 3,129,278 WEATHER SEALED AND SHIELDED DOUBLE DOOR CONSTRUCTION FOR RADIO FRE- QUENCY SHELTERS Charles E. Watt, Jr., Chelmsford, and Charles J. Carson,

Danvers, Mass., assignors to Craig Systems, Inc., Lawrence, Mass a corporation of Massachusetts Filed Jan. 30, 1963, Ser. No. 255,031 5 Claims. (Cl. I'M-35) Our invention relates to radio frequency shielded shelters, and particularly to an improved double door construction for shelters of this kind which provides an effective weather seal and greatly attenuates incident electromagnetic energy at communication frequencies.

It is frequently necessary in the use, maintenance and testing of electronic equipment to provide an environment free of externally generated electromagnetic energy. The basic principle upon which shelters for providing such an environment have been constructed involves the enclosure of the apparatus to be shielded in a shell of electrically conductive material possessing a combination of electromagnetic and radio wave reflective properties. The application of this principle to the construction of simple shielding panels, such as walls and the like, is relatively simple. However, in the construction of mobile radio frequency shielded shelters which are to be used in the field under a wide range of environmental conditions, it is also necessary to provide ventilation, air conditioning and temperature control, and suitable doors for ingress and egress. Door openings for this purpose must be provided with doors and door seals which can be readily closed to form an efilcient electromagnetic shield and an effective watertight, weather-tight seal even under the most adverse circumstances, as when exposed to wind-driven rain. Also, the door seals should desirably provide an airtight seal so that nominal positive air pressures can be built up inside the shelter, to prevent in leakage, and to ensure chemical, biological and radiological warfare protection for operating personnel by excluding contaminants. Especially for use in polar regions, a double, commonly called a Dutch door, would be highly desirable, because snow or ice may be allowed to pile up around a shelter provided with such a door, to an extent which would prevent the opening of a full length door, without impeding the operation of the upper portion of the double door. A double door is also useful on shelters which are to be operated in place on a transporting vehicle, in which an obstruction, such as a tailgate, would impede the opening of a full sized one piece door, and the use of only a portion of the maximum door opening under adverse climactic conditions would make it easier to maintain controlled conditions of temperature, pressure and humidity within the shelter. It is the object of our invention to make it possible to use a double door construction in a radio frequency shielded shelter without reducing the overall attenuation of externally generated electromagnetic energy by the shelter when the doors are in closed position. Briefly, a double door construction in accordance with our invention comprises means for establishing a complete electrical circuit, as an integral part of the door seal, between the conducting door panels of a double door and the conducting frame of a metal building to which the doors are attached. At the same time, means are provided for completely sealing the shelter when the doors are in closed position, to exclude the elements and to minimize the exchange of air, heat or moisture between the inside and outside of the shelter around the edges of the doors. In accordance with the preferred embodiment of our invention, the construction includes means let into the 3,129,278 Patented Apr. 14, 1964 door frame and cooperating with conducting and sealing elements on the doors for completing an electrical connection between the doors and the building when the doors are closed, and at the same time completing a weather seal. An important advantage of a double door constructed in accordance with the preferred embodiment of our invention is that the conductive elements which electrically connect the doors to the frame are themselves sealed against the effects of ambient temperature, moisture, and airborne contaminants or corrosive elements such as salt spray when the doors are closed.

Our invention will best be understood in the light of the accompanying drawings, together with the following detailed description, of a preferred embodiment thereof.

In the drawings,

FIG. 1 is a fragmentary diagrammatic sketch of a radio frequency shelter employing double doors constructed in accordance with the preferred embodiment of our invention;

FIG. 2 is a fragmentary front view of a portion of the front of the building shown in FIG. 1, with the doors in closed position, and with parts broken away to show the construction of the doors;

FIG. 3 is a fragmentary sectional plan view taken essentially along the lines 3-3 in FIG. 2;

FIG. 4 is a fragmentary sectional view taken essentially along the lines 4-4. in FIG. 2; and

FIG. 5 is a fragmentary diagrammatic sketch, with parts shown in section and parts broken away, showing a detail of the door construction of FIGS. 14 at the junction between the doors.

Referring first to FIG. 1, we have shown a metal building 1, which, except for the portions described in detail below, may be assumed to be constructed in the conven tional manner for such shelters, of aluminum or steel sheets welded, bolted or bonded to suitable aluminum framing members, with suitable conventional expedients adopted for sealing and electromagnetically shielding the corners and panel joints. The front of this building is shown provided with a door opening defined by a frame, which may comprise a channel member 3, as best shown in FIGS. 1 and 5. Referring to FIG. 5, the edges of the channel 3 may be attached to metal walls 5 and 7 to form a box wall structure with both metal walls connected by an electrical conductive path including the channel member 3. The space between the wall panels 5 and 7 may be filled with any conventional insulating material of suitable structural properties, such as foamedin-place polyurethane insulation, styrofoam, paper or fabric honeycomb material saturated with a suitable resin, or the like, as indicated at 9.

Referring again to FIG. 1, the door opening defined by the frame 3 is adapted to be closed by double doors comprising an upper door 11 and a lower door 13. These doors are provided with suitable hinges, such as the hinge 15, which are pinned to rotate about axes sufficiently displaced from the frame that the doors will be essentially flush with the frame as they approach closed position. The doors are provided with suitable radio frequency attenuating external operating handles such as 17, which are provided on the inside with lugs, such as the lug 19. The lugs such as 19 cooperate with suitable cam means, such as the nylon block 21 shown attached to the rear of the frame 3. The block 21 is provided with an inclined surface, so that upon rotation of one of the handles such as 17, the associated lug 19 will be wedged into engagement with the block 21 to forcibly hold the doors against the frame. Inner handles 18 are provided to facilitate opening the doors from within.

As indicated in FIG. 1, the door handles 17 may be provided with stop brackets, as at 23, which serve as sup- 3 ports for padlocking the doors in their closed position during shipment. These brackets may be attached by any suitable means. By using the wing nuts 25 it is possible for personnel to get out of the shelter if the door is accidentally padlocked from outside. Bolts, generally designated by 27, may be provided if desired to make it possible for personnel within the building to prevent opening of the doors from the outside.

The door 11 is provided around its outer edges with a continuous flexible weather strip 29, of any suitable compressible insulating material, such as sponge rubber or the like, which is secured to the door in a manner to be described. Within this weather strip is a continuous strip 31 of flexible knitted or woven metal wire mesh. This strip, which is employed to secure an electrical connection between the doors and the frame of the building, may be made in a conventional manner from a sheet of knitted or woven metal wire mesh, by rolling it upon itself and securing it in a roll by a sleeve knitted. around it in the well known manner used to knit stockings, to create a compressible radio frequency sealing gasket of circular cross section.

Preferably, the metal strip 31 is made to have a substantially higher compressive stiffness than the weather strip 29, to ensure that, in compressing the weather strip sufficiently topovide a seal, a good electrical connection, preferably at a pressure of about 20 p.s.i., is made between the strip, the frame, and the door. For example, in one practical embodiment of our invention, the metal strip had a compressive stiffness of 14 pounds per lineal inch, and the compressive stiffness of the weather strip was 4 pounds per linear inch.

Referring now to FIG. 4, the details of the construction of the edges of the upper and lower doors are shown. The upper door 11 may be made from a channel 33, to the edges of which are secured an inner panel 35 and an outer panel 37 by any suitable fastening and sealing means which provides for a very low resistance electrical path between the channel and inner and outer panels. The box construction so formed may be filled with any desired structural insulating material, preferably the same as that used in the wall construction described above, which will produce with the wall panels of the door a sandwich construction of suitable structural strength. As indicated in FIG. 4, the top of the door 11 formed by the channel 33 is grooved to receive the weather strip 29 and the woven metal strip 31, which may be secured in place by the reentrant edges of the grooves.

The construction of the lower door 13 is essentially the same as that of the upper door 11, except that it includes an additional channel member 39. The channel member 39 is bolted to the upper edge of the door, which is formed by a channel member 41, by suitable means such as the bolts 43 and 45. As shown, the channel member 3 extends above the top of the lower door 13 to form a frame for the lower edge of the door 11. The lower door is also provided with an outer weather strip 47, of rubber or the like, and an inner strip 49 of woven metal wire mesh, in the same manner as the upper door. As indicated in FIG. 4, the bolt 45 extends through the weather strip 47, as do other such bolts as it may be desirable to provide, so that there is no interruption in the seal at the fastening points.

It will be apparent that by the above construction, when the doors 11 and 13 are in their closed position, the junction between the doors is completely sealed by the weather strips 29 and 47 which are in contact with the edges of the doors and with the channel 39. An electrical connection is established between the channel 33 forming part of the door 11, and the channel 41 forming a part of the door 14, by the electrical path which includes the woven metal strip 31, the channel member 39, and the woven metal strip 49. At the same time, the other edges of the doors 11 and 13 are sealed and electrically A connected to the frame 3 by the weather strips 29 and 47, and the metal strips 31 and 49, respectively.

The strips described above suffice to seal and shield all the construction described above with the exception of the corners at the junctions of the doors 11 and 13 and the frame 3. These junctions are sealed and shielded by bridge members best shown in FIGS. 1, 3 and 5. Referring first to FIG. 3, the channel member 3 forming the door frame is cut away on either side to provide openings to receive two weather bridge members 51, one on each side, of rubber or the like, and preferably of the same material as the strips 29 and 47. Surrounding each bridge member 51 is a second bridge member 53 of woven metal wire mesh. These members may be secured in the frame by a metal block such as 55. Preferably, the block is so constructed, and the bridge members are so shaped, that they are held in interlocking manner to protrude somewhat beyond the front and side edges of channel 3, as schematically indicated. As indicated in FIG. 5, in the closed position of the doors the weather strips 29 and 47 are connected on each side by one of the bridge members 51, whereas the mesh wire strips 31 and 4 are connected on each side by one of the bridge members 53.

Referring now to FIG. 3, the channel 39 is provided with tapered ends, as at 57 and 59, which wedge into firm engagement with the weather'bridges 51 and the woven metal wire bridge members 53. Thus, in the closed position of the doors, there is a complete weather seal around all the joints, and each of the metal members at each joint has a direct low impedance electrical connection with each of the other members at the junction. We have found that this construction makes it possible to achieve attenuation of at least 47 decibels, in the frequency range of kilocycles to 10,000 megacycles, in a shelter which is otherwise sufiiciently shielded.

While we have described one embodiment of our invention in detail, many changes and variations will occur to those skilled in the art upon reading our description, and such can obviously be made without departing from our invention.

Having thus described our invention, what we claim is:

1. An electromagnetically shielded double door construction, comprising a conductive frame defining an opening, first and second conductive doors hinged to said frame for movement between open positions and a closed position in which the doors fill the opening, each engaging the frame on three sides and having a fourth side adjacent the fourth side of the other, a framing member attached to the fourth side of one door to form a frame for the fourth side of the other with both doors in closed position, a flexible weather strip secured to the edges of each door in position to contact said frame and framing member, a flexible strip of woven metal wire secured to each door within the confines of said weather strip and in position to contact said frame and framing member, two fiexible weather bridge members secured in said frame on each side adjacent the junction of said doors in closed position and adapted to contact said weather strips and the ends of said framing member, a flexible bridge of woven metal wire surrounding each weather bridge member and secured in the edge of the frame in position to bridge the flexible woven metal wire strips on the doors in their closed position, and means for securing the doors in their closed position to compress said strips and bridge members together and form a unitary sealed and electromagnetically shielded structure.

2. In a radio frequency shielded structure for providing an enclosed space free from externally generated electromagnetic radiation, a conductive door frame defining an opening, first and second doors hinged to said frame and movable between open positions and closed positions in which the opening is closed by the doors with three edges of each door engaging the frame and the remaining edges of the doors in close proximity, a

framing member secured to one of said remaining edges to form a frame contacting the remaining edge of the other door, an inner strip of woven metal wire secured to the periphery of each door in position to contact the frame and framing member, an outer weather strip of flexible insulating material surrounding the metal wire strip and attached to the periphery of each door in position to contact the framing member, a flexible weather sealing bridge member let into the frame on either side adjacent the juncture of said doors, in position to contact the ends of said framing member and both of said weather strips in the closed position of said doors, and two woven metal wire bridge members, each let into the frame and surrounding one of said weather bridge members on three sides with ends in position to contact both of said woven metal wire strips in the closed position of said doors.

3. Apparatus for sealing and electromagnetically shielding the junction of two adjacent conductive panels having abutting edges with a conductive member extending along an edge of each panel intersecting the abutting edges, comprising an outer flexible weather sealing strip around the edge of each panel in position to contact said conductive member, an inner strip of woven metal wire mesh around the edge of each panel within the weather strip and in position to contact said conductive member, a flexible weather bridge let into said conductive member and extending outwardly in position to contact both of said weather strips, a bridge member of woven metal wire mesh surrounding the weather bridge on three sides, let into said frame and extending outwardly in position to contact said wire mesh strips, and a second conductive member fastened to the abutting edge of one of said panels overlying said strips, said second conductive member having a protruding edge adapted to contact the strips on the other panel and an end formed to contact said weather bridge.

4. Apparatus for sealing and electromagnetically shielding the junction of two adjacent metal door panels having abutting edges with a metal door frame extending along an edge of each panel intersecting the abutting edges, comprising an outer flexible weather strip around the edge of each panel and contacting the frame, an inner flexible strip of electrically conductive material around the edge of each panel within the weather strip and contacting the frame, a conductive framing member secured to the abutting edge of one of said panels, overlying the strips on the panel, and protruding beyond the panel to overlie and contact the strips on the other panel, said frame member having an end confronting the junction of said doors and frame and inclined away from the junction, a bridge member of flexible insulating material contacting the doors, the frame, and said end of the framing member and overlying the flexible weather strips on said doors, and a bridge member of flexible electrically conductive material connecting the electrically conductive strips on said doors and the frame.

5. The apparatus of claim 4, in which the compressive stiffness of the electrically conductive strips is substantially greater than that of the weather sealing strips.

No references cited. 

3. APPARATUS FOR SEALING AND ELECTROMAGNETICALLY SHIELDING THE JUNCTION OF TWO ADJACENT CONDUCTIVE PANELS HAVING ABUTTING EDGES WITH A CONDUCTIVE MEMBER EXTENDING ALONG AN EDGE OF EACH PANEL INTERSECTING THE ABUTTING EDGES, COMPRISING AN OUTER FLEXIBLE WEATHER SEALING STRIP AROUND THE EDGE OF EACH PANEL IN POSITION TO CONTACT SAID CONDUCTIVE MEMBER, AN INNER STRIP OF WOVEN METAL WIRE MESH AROUND THE EDGE OF EACH PANEL WITHIN THE WEATHER STRIP AND IN POSITION TO CONTACT SAID CONDUCTIVE MEMBER, A FLEXIBLE WEATHER BRIDGE LET INTO SAID CONDUCTIVE MEMBER AND EXTENDING OUTWARDLY IN POSITION TO CONTACT BOTH OF SAID WEATHER STRIPS, A BRIDGE MEMBER OF WOVEN METAL WIRE MESH SURROUNDING THE WEATHER BRIDGE ON THREE SIDES, LET INTO SAID FRAME AND EXTENDING OUTWARDLY IN POSITION TO CONTACT SAID WIRE MESH STRIPS, AND A SECOND CONDUCTIVE 